Viruses, Viroids, and Prions 13 Viruses, Viroids, and Prions

Attachment, Penetration, and Uncoating Pinocytosis Figure 13.14a

Attachment, Penetration, and Uncoating Fusion Figure 13.14b

Release of an Enveloped Virus by Budding Figure 13.20

Multiplication of DNA Virus Figure 13.15

+ Sense Strand (+ Strand) RNA Virus Maturation and release Entry and uncoating Translation and synthesis of viral proteins RNA replication by viral RNA- dependent RNA polymerase Uncoating releases viral RNA and proteins. Nucleus Attachment Viral protein Capsid Cytoplasm Host cell – strand is transcribed from + viral genome. + strand mRNA is transcribed from the – strand. RNA genome (RNA) ssRNA; + or sense strand; Picornaviridae (a) Figure 13.17a

— Antisense Strand (— Strand) RNA Virus Maturation and release Entry and uncoating Translation and synthesis of viral proteins RNA replication by viral RNA- dependent RNA polymerase Uncoating releases viral RNA and proteins. Nucleus Attachment Viral protein Capsid Cytoplasm Host cell – strands are incorporated into capsid The + strand (mRNA) must first be transcribed from the – viral genome before proteins can be synthesized. Additional – strands are transcribed from mRNA. RNA genome (RNA) ssRNA; – or antisense strand; Rhabdoviridae (b) Figure 13.17b

Double-Stranded RNA Virus Maturation and release Entry and uncoating Translation and synthesis of viral proteins RNA replication by viral RNA- dependent RNA polymerase Uncoating releases viral RNA and proteins. Nucleus Attachment Viral protein RNA polymerase initiates production of – strands. The mRNA and – strands form the dsRNA that is incorporated as new viral genome. Cytoplasm Host cell mRNA is produced inside the capsid and released into the cytoplasm of the host. Capsid RNA genome (RNA) dsRNA; + or sense strand with – or antisense strand; Reoviridae Capsid proteins and RNA- (c) Figure 13.17c

Pathways of Multiplication for RNA-Containing Viruses Figure 13.17

Multiplication of a Retrovirus PLAY Animation: Viral Replication Figure 13.19

DNA and RNA Viruses Compared DNA: Cellular enzyme transcribes viral DNA in nucleus. DNA, reverse transcriptase: Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA. RNA, + strand: Viral RNA is a template for synthesis of RNA polymerase.

DNA and RNA Viruses Compared RNA – strand: Viral enzyme copies viral RNA to make mRNA in cytoplasm. RNA, double-stranded: Viral enzyme copies – strand RNA to make mRNA in cytoplasm. RNA, reverse transcriptase: Viral enzyme copes viral RNA to make DNA in cytoplasm.

Cancer Activated oncogenes transform normal cells into cancerous cells. Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens. The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.

Oncogenic Viruses Oncogenic DNA viruses Adenoviridae Heresviridae Poxviridae Papovaviridae Hepadnaviridae Oncogenic RNA viruses Retroviridae Viral RNA is transcribed to DNA which can integrate into host DNA HTLV 1 HTLV 2

Latent viral infections Virus remains in asymptomatic host cell for long periods. Cold sores, shingles Presistent viral infections Disease processes occurs over a long period; generally is fatal. Subacute sclerosing panencephalitis (measles virus) Figure 13.21

Prions Infectious proteins Inherited and transmissible by ingestion, transplant, and surgical instruments Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease PrPC: Normal cellular prion protein, on cell surface PrPSc: Scrapie protein; accumulates in brain cells forming plaques PLAY Animation: Prion Reproduction

Prions Figure 13.22

Plant viruses: Enter through wounds or via insects. Viroids: Infectious RNA; e.g., potato spindle tuber disease. Figure 13.23

Some Plant Viruses Table 13.6

Virus Families Single-stranded DNA, nonenveloped viruses Parvoviridae Human parvovirus Fifth disease Anemia in immunocompromised patients Table 13.2 (1 of 20)

Double-Stranded DNA, Nonenveloped Viruses Mastadenovirus Respiratory infections in humans Tumors in animals Table 13.2 (2 of 20)

Double-Stranded DNA, Nonenveloped Viruses Papillomavirus (human wart virus) Polyomavirus Cause tumors; some cause cancer Table 13.2 (3 of 20)

Double-Stranded DNA, Enveloped Viruses Orthopoxvirus (vaccinia and smallpox viruses) Molluscipoxvirus Smallpox Molluscum contagiosum Cowpox Table 13.2 (4 of 20)

Double-Stranded DNA, Enveloped Viruses Simplexvirus (HHV1 and HHV 2) Varicellavirus (HHV 3) Lymphocryptovirus (HHV 4) Cytomegalovirus (HHV 5) Roseolovirus (HHV 6) HHV 7 Kaposi's sarcoma (HHV 8) Some herpesviruses can remain latent in host cells. Table 13.2 (5 of 20)

Double-Stranded DNA, Enveloped Viruses Hepadnavirus (Hepatitis B virus) Use reverse transcriptase to produce DNA from mRNA. Table 13.2 (6 of 20)

Single-Stranded RNA, + Strand, Nonenveloped Enterovirus Enteroviruses include poliovirus and coxsackievirus. Rhinovirus Hepatitis A virus Table 13.2 (7 of 20)

Single-Stranded RNA, + Strand, Nonenveloped Hepatitis E virus Norovirus causes gastroenteritis. Table 13.2 (8 of 20)

Single-Stranded RNA, + Strand, Enveloped Alphavirus Alphaviruses are transmitted by arthropods; include EEE, WEE. Rubivirus (rubella virus) Table 13.2 (9 of 20)

Single-Stranded RNA, + Strand, Enveloped Arboviruses can replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses Hepatitis C virus Table 13.2 (10 of 20)

Single-Stranded RNA, + Strand, Enveloped Coronavirus Upper respiratory infections SARS Table 13.2 (11 of 20)

Single-Stranded RNA, – Strand, One RNA Strand Vesiculovirus Lyssavirus (rabies virus) Cause numerous animal diseases Table 13.2 (12 of 20)

Single-Stranded RNA, – Strand, One RNA Strand Filovirus Enveloped, helical viruses Ebola and Marburg viruses Table 13.2 (13 of 20)

Single-Stranded RNA, – Strand, One RNA Strand Paramyxovirus Morbillivirus Parainfluenza Mumps Newcastle disease Table 13.2 (14 of 20)

Single-Stranded RNA, – Strand, One RNA Strand Hepatitis D virus Depends on coinfection with Hepadnavirus Table 13.2 (15 of 20)

Single-Stranded RNA, – Strand, Multiple RNA Strands Influenzavirus (Influenza viruses A and B) Influenza C virus Envelope spikes can agglutinate RBCs. Table 13.2 (16 of 20)

Crossing the Species Barrier UN 13.3

Single-Stranded RNA, – Strand, Multiple RNA Strands Bunyavirus (CE virus) Hantavirus Table 13.2 (17 of 20)

Single-Stranded RNA, – Strand, Multiple RNA Strands Arenavirus Helical capsids contain RNA-containing granules Lymphocytic choriomeningitis VEE and Lassa Fever Table 13.2 (18 of 20)

Single-Stranded RNA, Two RNA Strands, Produce DNA Lentivirus (HIV) Oncogenic viruses Use reverse transcriptase to produce DNA from viral genome. Includes all RNA tumor viruses Table 13.2 (19 of 20)

Double-Stranded RNA, Nonenveloped Reovirus (Respiratory Enteric Orphan) Rotavirus Mild respiratory infections and gastroenteritis Colorado tick fever Table 13.2 (20 of 20)